溶融塩化物中におけるNiおよびFeの腐食の電気化学的研究

抄録

Electrochemical studies of corrosion of Ni, Fe and their alloys have been made in molten chloride at 973 K by using potentiodynamic polarization, rotating disk electrode and polarization resistance methods. From the polarization experiments it was concluded that metallic corrosion in molten chloride occurs only in the presence of water, oxygen or other oxidants. The cathodic reduction of oxygen proceeds via a two-step reaction (O₂+2e→O₂²⁻ and O₂²⁻+2e→2O²⁻), exhibiting two current waves. In the presence of water, however, oxygen is reduced as O₂+2H₂O+4e→4OH⁻. Although metallic corrosion in molten chloride is generally caused by dissolved oxygen, it is greatly accelerated by the presence of water. Anodic dissolution current of Ni in molten chloride decreased with increasing concentration of carbonate (oxide) up to 0.5 mol%, whereas it incresed with increasing carbonate over 1 mol%. This complicated effect of carbonate was well explained by the acidic and basic fluxing model for the dissolution of NiO. The results of the polarization experiment correspond well to those obtained from mass loss measurements. The instantaneous rate of corrosion of Ni, Fe and their alloys in molten chloride was estimated by the electrochemical polarization resistance method. The results indicated that the corrosion resistance of Ni and Fe was somewhat improved by alloying with Cr or Mo.